DE 26 52 506 discloses an electrical high current switch with liquid metal. On the one hand, a liquid metal mixture is used for wetting the solid metal electrodes and for reducing the contact resistance. Here the liquid metal is driven against the force of gravity by mechanical displacement, for example by movable contacts or pneumatically driven plunger pistons into the contact gap. The liquid metal can be additionally stabilized and fixed in the contact gap by the pinch effect according to which a current-carrying conductor undergoes radial striction by the current which is flowing through it. External magnetic fields and magnetic stray fluxes, for example by current feeds, can cause flow instabilities in the liquid metal and are shielded and are optionally allowed during disconnection in order to support extinguishing of the arc in the liquid metal.
The disadvantage is that gradual current limitation is not possible and arcs between the solid electrodes cause oxidation in the liquid metal. The design of the high current switch comprises seals for liquid metal, inert gas or a vacuum, and is accordingly complex.
DE 40 12 385 A1 discloses a current-controlled interrupting device with an operating principle which is based on the pinch effect with liquid metal. There is an individual, narrow, liquid metal-filled channel between the two solid metal electrodes. For an overcurrent the liquid conductor as a result of electromagnetic force is constricted by the pinch effect so that the current itself pinches and separates the liquid conductor. The displaced liquid metal is collected in a storage tank and after the overcurrent event flows back again. Contact separation takes place without an arc. But the device is only suited for relatively small currents, low voltages and slow interruption times, and therefore does not offer a lasting off state.
DE 199 03 939 A1 discloses a self-recovering current limiting means with liquid metal. There is a pressure-proof insulating housing between the two solid metal electrodes; in it there is liquid metal in the compressor spaces and in the connecting channels which lie in between and which connect the compressor spaces, so that there is a current path for nominal currents between the solid electrodes. In the connecting channels the current path is narrowed relative to the compressor spaces. The connecting channels are greatly heated during short circuit currents and evolve a gas. Avalanche-like gas bubble formation in the connecting channels vaporizes the liquid metal into the compressor spaces so that a current limiting arc is ignited in the connecting channels from which liquid metal has now been removed. After decay of the overcurrent the liquid metal can condense again and the current path is again ready for operation.
WO 00/77811 discloses a development of the self-recovering current limiting means. The connecting channels are conically widened to the top, so that the fill level of the liquid metal can be varied and the rated current carrying capacity can be changed over a wide range. Moreover, a meandering current path is formed by an offset arrangement of the connecting channels so that in overcurrent-induced vaporization of the liquid metal a series of current-limiting arcs is ignited. These pinch effect current limiters require a structure which is very stable with respect to pressure and temperature; this is structurally complex. Major wear within the current limiters occurs due to current limiting by arc and burn-off residues can contaminate the liquid metal. Recondensation of the liquid metal causes a conductive state immediately after a short circuit so that there is no off state.
This application refers to the prior art which is disclosed in utility model DE 1 802 643. It shows a call device for filling stations in which a bell switch is electrically closed by a liquid metal by a vehicle rolling over an air-filled hose and it's thus being compressed such that the escaping air moves the liquid metal column between the bell contacts. The liquid metal is moved purely passively by an external action, specifically by a vehicle which is to be detected. Since the liquid metal column which is captured in the hose acts as a vehicle detector, there is no self-contained control for specific opening and closing of the switch by means of the liquid metal.